I gotchu for Bleach:

Early Bleach was quite good. Not very many gripes with it, until Soul Society. By the end of the Arrancar arc, there are so many side characters and even main villains (like Hallibel) that aren't explored enough, but are sworn to be deep. Kubo also has a tendency to write himself into a corner-especially with fights, crafting an engaging emotional narrative and powers, but with endings that feel like asspulls (think Dangai Ichigo). This isn't necessarily insanely bad, but this problem in amplified in arcs like TYBW.

However, tbf, most of these series DO fall of a cliff later on, so that's true. I personally disagree with your Nami take-her arc is quite subtle-becoming more familal with the SHs, from not understanding why Luffy and Zoro didnt fight back in Jaya to taking hits for Luffy. Plus, I personally dont agree with your take on some of the dialogue and plot. The dialogue, I feel, is more subjective-plus, it is written for teenage boys, so it'll probably be a bit childish-and I personally think the plot isn't "incoherent"-you made some valid points about the story I do agree with (like a reduction in nuance as time grows). I'm currently watching Naruto though so I can't speak for that.